1. Field of the Invention
This invention relates to a composite hydrogen storage alloy material and a method of producing the same.
2. Description of the Prior Art
In recent years, there has been a great deal of attention focused on use of fossil fuels such as heavy oil, gasoline and the like as the main cause of air pollution and earth anathermal phenomenon, and hydrogen gas has attracted attention as an alternate clean energy source. Especially hydrogen storage alloys for storing hydrogen gas have been marked.
The hydrogen storage alloy stores and transports hydrogen by hydrogenation and dissociation of metal. It is preferred that the hydrogen storage alloy can store as much hydrogen as possible. Mg-based hydrogen storage alloys which can occlude 7.6 wt % of hydrogen have been known as hydrogen storage alloy having a large hydrogen storage capacity.
An example of the Mg-based hydrogen storage alloys is disclosed in Japanese Unexamined Patent Publication No. 63(1988)-72849. The Mg-based hydrogen storage alloy is formed by depositing a predetermined amount of ultrafine particles of Ni on Mg-Ni alloy powder, and in the Mg-based hydrogen storage alloy, a catalytic effect of Ni increases the hydrogen storing speed and the hydrogen releasing speed.
However the Mg-based hydrogen storage alloy is disadvantageous in that it must be subjected, before use, to an initial activation process in which the alloy is heated to about 400.degree. C. in pure hydrogen and deaeration and hydrogenation are repeated in order to remove gases adsorbed on the surface of the alloy, e.g., H.sub.2 O, CO, CO.sub.2 and the like, and to facilitate storing and release of hydrogen, and that it can neither store nor release hydrogen unless heated to about 300.degree. C.
When a high temperature is necessary for the initial activation process and storage and release of hydrogen, the reservoir for accommodating the hydrogen storage alloy must have a very high high-temperature rigidity, which adds to the weight of the reservoir.
Further such hydrogen storage alloy as operates at a high temperature can be used only a limited place. For example, when such hydrogen storage alloy is used as the fuel source for a hydrogen engine vehicle, the overall weight of the vehicle becomes excessively large due to the weight of the hydrogen storage alloy and the reservoir for the alloy, which results in deterioration of fuel economy. Further in the case of a vehicle, it is difficult to provide a heat source for heating the alloy to such a high temperature, and generally it is not preferred that such a high-temperature heat source is mounted on a vehicle.